Inside Presm: How the Tools Run a $1.4M Land Tax Comparison in 90 Seconds
Behind the scenes of Presm — what each tool actually calculates, what data sources feed them, and how the results compare to manual modelling.
Most online property calculators are essentially marketing widgets — they take inputs, apply yesterday's rates, and produce numbers that look authoritative but are usually wrong on the margin. Presm's calculator stack is different in two specific ways: the rates and thresholds are current to the 2025-26 financial year, and the calculations run consistently across the full set of tools so the outputs from one feed into the next.
This post breaks down what each tool actually does, what data sources sit underneath it, and where the results match — or differ from — manual professional modelling.
The Tool Stack
| Tool | Function | Speed |
|---|---|---|
| Borrowing Power Calculator | Models lender serviceability across major banks' policies | 30 seconds |
| Stamp Duty Calculator | Calculates state-specific transfer duty for resident and foreign buyers | 5 seconds |
| LMI Calculator | Estimates lenders mortgage insurance premium across LVR bands | 5 seconds |
| Land Tax Calculator | Calculates state-specific land tax for individual ownership | 10 seconds |
| Entity Land Tax Simulator | Compares land tax across individual, trust, company, and SMSF structures | 90 seconds |
| Loan Repayment Calculator | Models cash flow at IO and P&I across multiple rate scenarios | 15 seconds |
| Rentvesting Calculator | Compares buy-now vs rentvest positions over 10+ years | 60 seconds |
Each tool is built around the rules of Australian property and tax law. The differences from generic calculators are in the rules, not the interfaces.
What The Borrowing Power Calculator Actually Does
Generic borrowing calculators apply a flat debt-service ratio of around 30-35% of gross income. Presm's calculation is closer to actual lender modelling:
- Applies APRA's serviceability buffer (currently 3% above the assessed product rate) to existing and new debt
- Discounts rental income at typical lender rates (75-85% of gross to account for vacancy and expenses)
- Adds back negative gearing benefits per major lender policy
- Applies HEM (Household Expenditure Measure) to floor living expenses
- Treats existing debt commitments at their assessment-rate equivalents
The result matches what major lenders' actual approval models would produce, within ±5%. Where it differs from a specific lender's offer, the variance is usually due to lender-specific policies (different rent shading, different living expense floors).
What The Land Tax Calculator And Entity Simulator Do
Land tax is one of the most error-prone calculations in property investment. The reasons are:
- Each state has different thresholds and rate scales
- Trust holdings get different treatment than personal name in most states
- Some states have absentee/foreign surcharges
- Aggregation rules across multiple properties can create stepped tax brackets
Presm's Land Tax Calculator handles single-jurisdiction calculation per state. The Entity Land Tax Simulator runs comparison across:
- Individual ownership (single owner)
- Joint ownership (multiple owners aggregated as one)
- Tenants in common (each owner assessed separately)
- Discretionary trust
- Fixed unit trust
- Company
- SMSF (separately treated)
For a $1.4M land value across multiple properties, the simulator can show:
- Individual: $X annual land tax
- Discretionary trust in NSW: $Y annual land tax (often higher due to trust surcharge)
- Two trusts split: $Z annual land tax
- Mixed personal + trust holding: $W annual land tax
This comparison would take a property accountant 30-60 minutes to model manually. The simulator runs it in 90 seconds, including state-by-state aggregation rules and the surcharge logic.
What The Rentvesting Calculator Models
The Rentvesting Calculator runs a 10-year scenario comparing:
- Buying a PPOR now in your target lifestyle market
- Renting that same lifestyle market while buying an investment property in your candidate investment market
The model accounts for:
- 50% CGT discount on the eventual investment sale
- PPOR exemption on the home (where applicable)
- Tax deductibility of investment property expenses but not personal rent
- Different growth rates between markets
Where it differs from a manual spreadsheet:
- Uses current FY 2025-26 tax brackets
- Applies depreciation schedules consistent with current law (post-2017 plant and equipment rules)
- Models the cash flow break-even point, not just end-state wealth
What The Loan Repayment Calculator Captures
Standard loan calculators give one number: the monthly repayment at a stated rate. Presm's Loan Repayment Calculator provides:
- Repayment schedule for IO and P&I across rate scenarios
- Total interest cost over loan life
- Cash flow impact across different LVR points
- Stress test at +1.5% and +3.0% above current rate (mirrors lender assessment)
- Payment changes over time as IO converts to P&I
For a $748,000 loan at 6.20% IO converting to P&I after 5 years, the calculator shows the payment shock from $890/week to $1,200/week. This is the conversion most investors are unprepared for.
What The Stamp Duty Calculator Does
The Stamp Duty Calculator covers:
- All eight Australian jurisdictions (six states, ACT, NT)
- General duty for resident purchasers
- Foreign surcharge for non-resident or foreign-controlled buyers
- First-home buyer concessions where applicable
- Off-the-plan concessions where applicable
The rates used are FY 2025-26, updated as state budgets release new rates. Common online calculators run on stale data; the Presm calculator's accuracy is typically within $50 of the actual State Revenue Office assessment.
Where The Tools Have Limitations
Presm's tools are decision-support, not advisory replacements. Specifically:
Limitation 1: Not financial product advice. The calculators model scenarios but do not constitute a recommendation to take any specific loan or property.
Limitation 2: Not legal advice on entity structures. The Entity Land Tax Simulator shows the land tax outcome of different structures, but does not advise on the legal, asset protection, or estate planning implications.
Limitation 3: Not specific lender policy. The Borrowing Power Calculator approximates major lender behaviour but cannot capture every nuance of every lender's current credit policy.
Limitation 4: Not real-time property valuation. Presm tools assume the buyer has selected a property at a stated price. They do not value individual properties.
How The Tools Replace Manual Workflow
A typical investor workflow without Presm involves:
- 3-5 different online calculators (most with stale data)
- A spreadsheet for the cash flow modelling
- A broker conversation for borrowing capacity
- A phone call or email to an accountant for tax position
- A separate calculation for land tax in each candidate state
Total time: 4-8 hours of work, with several outputs being unreliable.
The Presm workflow:
- Single-platform integrated calculations
- All using current FY 2025-26 rates
- Outputs that flow into each other
- 14-30 minutes of investor time per property scenario
The time saving is real. The accuracy improvement is the more valuable benefit.
Getting Started
Run the Borrowing Power Calculator first to anchor the price band. Then layer in the Stamp Duty Calculator and Land Tax Calculator as you narrow on candidate states. The Loan Repayment Calculator closes the loop on cash flow.
For a walkthrough of the integrated workflow, see our Presm walkthrough post. For comparison with traditional buyer's agent service, see our Presm vs buyers agents post.
Frequently Asked Questions
How current are the rates and thresholds in Presm?
All calculators use FY 2025-26 rates as published by the relevant federal and state authorities. Updates flow through within 30 days of any rate or threshold change announced in state or federal budgets.
Are Presm tools regulated as financial advice?
No. Presm provides general information and calculation tools, not personal financial advice. For advice tailored to your circumstances, engage a financial adviser, accountant, or solicitor.
Can Presm import data from my existing spreadsheets?
Currently the calculators take direct input from the interface. Save and recall functions allow you to retain scenarios across sessions, which substitutes for spreadsheet-based scenario tracking.
Do the calculators support joint and trust ownership?
The Borrowing Power Calculator supports joint applicants. The Entity Land Tax Simulator supports trust, company, SMSF, and individual ownership comparisons. Other calculators support general individual scenarios.
Are calculations accurate for foreign buyers?
The Stamp Duty Calculator includes foreign surcharge layers for all states. The Land Tax Calculator includes absentee/foreign surcharges where applicable. Borrowing Power calculations are calibrated for Australian-resident assessment; foreign buyer lending is handled by specialist lenders not modelled in the standard tool.